Count the number of even sum subarrays in an array

even_pairs.cc

#include <iostream>
#include <vector>

using namespace std;

int even_pairs(const vector<bool> &v) {
    int even_now = 0, odd_now = 0;
    int total = 0;
    for (bool x : v) {
        int even_before = even_now;
        int odd_before = odd_now;
        if (!x) {
            even_now = even_before+1;
            odd_now = odd_before;
        } else {
            even_now = odd_before;
            odd_now = even_before+1;
        }
        total += even_now;
    }
    return total;
}

int main(void) {
    int m;
    cin >> m;
    while(m--) {
        int n;
        cin >> n;
        vector<bool> vec;
        vec.reserve(n);
        while (n--) {
            int num;
            cin >> num;
            vec.push_back(num);
        }
        cout << even_pairs(vec) << endl;
    }
}